Estimating the stresses in cantilever beam loaded by a parabolically distributed load with Airy stress functions

This study presents three mathematical methods namely the polynomial stress function approach, the Fourier series form approach and the approximated equations form approach for finding the stress distribution in a cantilever beam with rectangular cross section loaded by a parabolically distributed load. By taking the stress function as a polynomial of the seventh degree, it is attempted to find the coefficients either in complete or in full shape of the polynomial. In the Fourier series approach, the load is discreted to unlimited series of harmonic loads and superposing resultant stresses is the affect of parabolically distributed load on the beam. The resultant stresses are compared with some approximated stress formulas which have been provided before. Finite element analysis are done for square, short, medium and long cantilever beams and the mathematical results of stress distribution in five different height of the beam was compared with FEM results. It was found good results for τ _yy and τ _xy in all cross section of the beams and acceptable results for τ _xx only in y = 0. It is found that discreting loads to even a limit number of harmonic loads and superposing the resultant stresses can give the distribution of τ _yy and τ _xy with the acceptable precision in medium and long cantilever beams with rectangular cross section.     

A weight function-critical plane approach for low-cycle fatigue under variable amplitude multiaxial loading

Low‐cycle fatigue data of type 304 stainless steel obtained under axial‐torsional loading of variable amplitudes are analyzed using four multiaxial fatigue parameters: SWT, KBM, FS and LKN. Rainflow cycle counting and Morrow's plastic work interaction rule are used to calculate fatigue damage. The performance of a fatigue model is dependent on the fatigue parameter, the critical plane and the damage accumulation rule employed in the model. The conservatism and non‐conservatism of predicted lives are examined for some combinations of these variables. A new critical plane called the weight function‐critical plane is introduced for variable amplitude loading. This approach is found to improve the KBM‐based life predictions.     

Reliability analysis of TLP tethers under impulsive loading

In the present study, reliability assessment of Tension Leg Platform (TLP) tethers against maximum tension (i.e. tension exceeding yield) has been carried out under combined action of extreme wave and impulsive forces. For this purpose, a nonlinear dynamic analysis of TLP has been carried out in time domain. A limit state function for maximum tension (i.e. tension exceeding yield) has been derived employing Von-Mises theory of failure. Using this derived limit state function and responses obtained after dynamic analysis under sinusoidal, half-triangular and triangular impulsive forces, reliability assessment of the TLP tethers has been carried out. Design point, important for probabilistic design of tethers, has been located on the failure surface after solving a constrained optimization problem. To study the influence of various random variables on tether reliability, sensitivity analysis has been carried out. Effects of angle of impact; effect of variable submergence; and effect of material yield strength on tether reliability have also been studied on parametric basis. Effect of uncertainty on overall tether reliability has also been discussed to show the importance of quality control in the various design parameters.     

Fully plastic J-integral solutions for surface cracked plates under biaxial loading

In this paper, surface cracked plates under biaxial tension are studied. Three-dimensional elastic-plastic finite element analyses have been carried out to calculate the J-integral for surface cracked plate for a wide range of geometry, biaxiality and material properties. Fully plastic J-integral solutions along the front of the surface cracks are presented for Ramberg-Osgood power law hardening material of n = 3, 5, 10 and 15. Geometries considered are a/c = 0.2, 1.0 and a/t = 0.2, 0.4, 0.6 and 0.8 and the biaxial ratios of 0, 0.5 and 1. Based on these results, the J-integral along the crack front for general elastic-plastic loading conditions can be estimated using the EPRI scheme. These solutions are suitable for fracture analyses for surface cracked plates under biaxial loading.     

Preparation and CO gas-sensing behavior of Au-doped SnO2 sensors

A study on the low-temperature CO gas sensors based on Au/SnO₂ thick film was reported. Au/SnO₂ powders, with different Au loading from 0.36 to 3.57 wt%, were prepared by a deposition-precipitation method. Thick films were fabricated from Au/SnO₂ powders. The Au/SnO₂ thick-film sensors exhibited high sensitivity to CO gas at relatively low operating temperature (83-210 °C). We also reported the effect of the Au loading in Au/SnO₂ on the CO gas sensing behavior. The optimal Au loading in as-prepared Au/SnO₂ was 2.86 wt%.     

圆柱形部件表面疲劳裂纹扩展仿真及分析

给出了一种利用有限元技术模拟周期性张力载荷作用下圆柱形部件内裂纹扩展过程的方法。首先利用一系列点定义裂纹前沿，据此形成包含奇异单元的二维有限元网格，再扩展为三维网格，然后利用有限元法进行应力应变分析，最后使用Paris定律计算局部扩展增量，以此来更新裂纹的形状和尺寸。该方法还能够自动地重复执行扩展仿真。文中还对具有不同半径比的椭圆形和具有不规则形状的初始裂纹的扩展过程进行了仿真和分析比较，以此来取得裂纹在扩展过程中的形状变化特征。     

短路型石英传感器的平面冲击响应

石英传感器已广泛应用于冲击应力波剖面的测量。对不同宽厚比短路型石英传感器在冲击作用下的动态响应特点进行了研究,试验结果表明:不同宽厚比短路型石英传感器的动态响应特点基本相同,其压电系数与冲击应力满足线性关系;传感器压电系数斜升幅度与宽厚比的关系为:当石英传感器的宽厚比大于1.4时,其压电电流的斜升幅度基本不随宽厚比变化,而小于1.4时,压电电流的斜升幅度受边缘效应的影响明显上升,这表明宽厚比小于1.4的石英传感器可应用于实际工程测量。     

载银纳米SiO2制备与抗菌性研究

在60%硫酸乙酯催化下TEOS水解,通过控制水解条件,得到担载体纳米SiO2。采用吸附法在其表面负载银,制备无机抗菌材料。用抑菌圈直径和杀菌率表征粉末抗菌性能,研究了吸附时间、硝酸银浓度及吸附温度与负载量的关系,并考查了焙烧温度等因素对抗菌性能的影响。研究发现,以离子形式存在的贵金属银的抗菌性能强,焙烧处理温度决定其离子溶出性与可重复使用次数。     

Java虚拟机中类装载机制的原理分析与应用研究

Java类的动态装载机制是Java虚拟机的一项核心技术,可以在运行时刻动态地加载或替换系统的某些功能模块,而不影响系统其它功能模块的正常运行。本文介绍了Java虚拟机中类的动态装载机制的原理、实现及应用,分析了类装载器的结构、用途,阐述了利用自定义类装载器装载并执行Java类的过程。     

热轧厂层流冷却系统存在的问题及改造

分析了武钢热轧厂层流冷却系统存在问题,采用调节水箱与调速水泵运行相结合的改造方案,并解决了变频电机轴承承载能力不够问题,从而满足了生产需要,提高了产品质量,降低了能耗。